In 3rd Generation Partnership Project (3GPP), studies have been carried out on LTE-Advanced (hereinafter, abbreviated as “LTE-A”). In LTE-A, the introduction of a bandwidth expansion technology called “carrier aggregation” (CA) has been discussed. In LTE-A CA, a plurality of component carriers (CC), each having a 20 MHz bandwidth, for example, are bundled. Thus, an approach aiming at high-speed transmission through aggregation of a plurality of carriers is taken in downlink (DL) and uplink (UL) channels in LTE-A CA. In LTE-A, the possibility of bandwidth expansion through the introduction of five CCs, i.e., up to a 100 MHz bandwidth has been discussed.
In this respect, studies have been carried out at the same time on a transmission power control method targeting UL CA. In the studies on UL transmission power control in LTE-A, the following matters (A) to (C) have been agreed. First, CC-specific transmission power control is performed (A). CC-specific (for each UL channel) maximum transmission power Pcmax, c, and user equipment (UE) specific (UE-specific) maximum transmission power Pcmax (upper limit value of total maximum transmission power for a plurality of CCs) are provided (B). In addition, when the transmission power of each UL channel transmitted on one CC exceeds the CC-specific (for each UL channel) maximum transmission power, control called power scaling, which reduces the transmission power of a UL channel, is performed (B). In addition, the power scaling is also performed when a total value of transmission power of UL channels transmitted on a plurality (all) of CCs exceeds the UE-specific maximum transmission power (when power limitation occurs) in simultaneous transmission of a plurality of UL channels. In UL CA, the power allocation priority rule for a plurality of UL channels when power limitation occurs in simultaneous transmission of a plurality of UL channels and power scaling thus occurs is agreed as follows:PUCCH>PUSCH with UCI>PUSCH without UCI(C).
In the priority rule mentioned above, PUCCH stands for Physical Uplink Control CHannel, and PUSCH stands for Physical Uplink Shared CHannel. UCI is an abbreviation for Uplink Control Information, and for example, includes the following control information, specifically. Namely, UCI includes acknowledgment/non acknowledgment (ACK/NACK), rank indicator (RI), channel quality information (CQI), pre-coding matrix indicator (PMI) and channel state information (CSI). A periodic or aperiodic transmission method is used for transmitting the information such as CSI and CQI.
In addition, the term “PUSCH with UCI” refers to a PUSCH on which UCI is multiplexed, and the term “PUSCH without UCI” refers to a PUSCH on which no UCI is multiplexed. Accordingly, when power scaling occurs in simultaneous transmission of a plurality of UL channels, the transmission power is allocated in the following order: the transmission power for PUCCH; the transmission power for PUSCH on which UCI is multiplexed; and the transmission power for PUSCH on which no UCI is multiplexed. This rule applies regardless of whether these channels are on the same CC or on different CCs.
When a plurality of PUSCHs on which no UCI is multiplexed (PUSCH without UCI) are present, and the total value of transmission power of UL channels transmitted on a plurality (all) of CCs exceeds the UE-specific maximum transmission power, the terminal operation that applies power scaling uniformly on the plurality of PUSCHs without UCI is used. Specifically, power scaling is performed in this case by multiplying the transmission power of a plurality of PUSCHs without UCI under the CC-specific power control by the same scaling weight (w_C(≦1)) between the CCs.
In addition, studies have been carried out on a power allocation rule used when power scaling in CA relating to a periodic or aperiodic sounding reference symbol (SRS) used for measuring (sounding) channel quality such as CQI occurs.
Non-Patent Literatures (hereinafter, abbreviated as “NPL”) 1 and 2 disclose a power scaling method used when the total transmission power of a plurality of SRSs simultaneously transmitted on a plurality of CCs exceeds the UE-specific maximum total transmission power (power limitation occurs), for example. Specifically, scaling processing with respect to the plurality of SRSs among the CCs is performed by reusing the same scaling weight (w_C) applied to the PUSCHs on which no UCI is multiplexed among the CCs, i.e., by multiplying the transmission power of the plurality of SRSs by the scaling weight (w_C). As a result, even when power limitation occurs in simultaneous transmission of SRSs on a plurality of CCs, the terminal can appropriately determine the SRS transmission power for each CC according to this rule. The SRS transmission power is set by providing an offset to the PUSCH transmission power. Thus, the method described above that applies the scaling weight (w_C) for PUSCHs without UCI to SRSs is a highly compatible approach.
Meanwhile, in LTE-A UL transmission, the introduction of CA and multi-input and multi-output (MIMO) transmission using multiple antennas has been decided. In the transmission power control in UL-MIMO, the transmission power controlled for each CC is allocated equally to an antenna port configured for each CC (transmission power controlled for each CC is equally scaled and then allocated to each antenna port). In this manner, the transmission power of a UL channel transmitted from each antenna port is determined. For example, as illustrated in FIG. 1, when two antenna ports are configured on a CC, the (total) transmission power (P0) for the applicable CC under CC-specific transmission power control is divided by two (by multiplying the (total) transmission power for the applicable CC by scaling weight w_A=½(≦1) in antenna port domain). The resultant transmission power after the scaling is equally allocated to the two antennas.
Accordingly, when CA and multiple-antenna (such as MIMO or diversity) transmission are both employed, CC-specific power control in the CC (frequency) domain, and power scaling processing in antenna port (spatial) domain are performed. Accordingly, the transmission power of each of a plurality of UL channels to be simultaneously transmitted using a plurality of CCs and multiple antennas is determined. Firstly, the total transmission power (total value of transmission power) of UL channels to be transmitted via multiple antennas is controlled for each CC in the CC (frequency) domain (1). Next, the total transmission power for each CC that is determined (controlled) in (1) is equally allocated to the configured antenna ports in the antenna port (spatial) domain (2).
As described above, the method disclosed in NPLs 1 and 2, which is the power scaling method used for a plurality of SRSs in CA during power limitation, is combined with the equal power allocation (power scaling) method in the antenna port domain when multiple antennas are used. Accordingly, it is possible to make power scaling rules used when the total transmission power of all SRSs transmitted using a plurality of CCs and a plurality of antenna ports exceeds the UE-specific maximum transmission power (when power limitation occurs) in a configuration employing CA and multiple-antenna (such as MIMO or diversity) transmission together. The SRS transmission power is equally scaled between CCs (frequencies) by using the power scaling weight (w_C) used for a plurality of PUSCHs without UCI between CCs (1). The transmission power is equally allocated between antenna ports by multiplying transmission power for each CC obtained as a result of scaling between CCs, by scaling weight w_A in the antenna port domain (2).
FIG. 2 illustrates a case where the number of CCs is two and each CC is configured with two antenna ports for SRS transmission. According to rule (1) mentioned above, transmission power P0 and P1 controlled respectively by CC#0 and CC#1 are multiplied by equal power scaling weight (w_C) between CCs for a plurality of PUSCHs without UCI. Accordingly, the transmission power of CC#0 and CC#1 is reduced to (w_C×P0) and (w_C×P1).
Next, according to rule (2) described above, the transmission power of antenna port #20 of CC#0, antenna port #21 of CC#0, antenna port #20 of CC#1, and antenna port #21 of CC#1 is determined to be (w_C×w_A×P0), (w_C×w_A×P0), (w_C×w_A×P1), and (w_C×w_A×P1), respectively, by using the equal scaling weight in antenna port domain (w_A=½).